Oxide evolution in ODS steel resulting from friction stir welding
Bird, Mathew J.
Brewer, Luke N.
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This thesis investigated the evolution of oxide particles caused by friction stir welding of oxide dispersion strengthened steel, MA956. Eight welding conditions were used of different rotation and traverse rates, resulting in a range of heat inputs affecting weld quality. Raman spectroscopy was used to identify and map the distribution of yttrium-aluminum oxide particles in cross sections of the welds. Electron microscopy and energy dispersive X-ray spectroscopy provided additional information on the size and spatial distribution of these oxides as a function of welding condition. As the heat input increased, the oxide particles grew in size and incorporated aluminum and oxygen from the matrix. This compositional change resulted in the formation of aluminum-rich oxides such as yttrium aluminum perovskite and yttrium aluminum garnet. The tool rotation rate was the largest contributor to oxide evolution, while traverse rate had less impact on oxide evolution. Higher heat input welding conditions also lowered the hardness of MA956 due to oxide evolution and grain growth.
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